1. Field of The Invention:
The present invention relates to thickened aqueous cleaning compositions and in particular to a bleach-containing aqueous cleaning composition having a polymer/surfactant thickening system.
2. Description of the Prior Art:
Much prior art has addressed attempts to develop a thickened bleach cleanser, and advantages associated therewith are well documented in the art. The efficacy of cleaning compositions applied to non-horizontal surfaces is greatly improved by formulations which are highly viscous, increasing the residence time of the cleanser. Splashing during application and use is minimized, and consumer preference for a thick product is well documented. Numerous approaches to thickening a cleaning composition are known and include increasing the concentration of dissolved components, adding suspended solids, modifying characteristics of the dissolved components to create liquid crystal or gel phases, or by adding polymeric organic thickening agents. As used herein, "polymer" means a macromolecule made up of a plurality of chemical subunits (monomers). The monomers may be identical or chemically similar, or may be of several different types. Unless a more specific term is used, "polymer" will be taken to include hetero- and homopolymers, and random, alternating, block and graft copolymers. "Copolymer" will be used to specifically refer to those macromolecules made from two different repeating chemical monomers.
For various reasons, the prior art thickened compositions are not commercially viable. In many instances, thickening is insufficient to provide the desired residence time on non-horizontal surfaces. Adding components, and/or modifying characteristics of dissolved components often creates additional problems with the composition, such as syneresis, which require adding further components in an attempt to correct these problems. A drawback that has hampered prior art polymer thickened hypochlorite bleaching compositions is the tendency of the hypochlorite to oxidize the polymer, reducing or destroying its thickening capability. Prior art thickened bleach products generally exhibit phase instability at elevated (100.degree. F.) and/or low (35.degree. F.) storage temperatures. Further difficulties exist with clay type inorganic polymeric thickening agents in that these tend to exhibit either false-bodied or thixotropic rheologies, which, at high viscosities, can result in a tendency to set up or harden. Many of the compositions employing polymeric thickeners require relatively high levels of costly polymers. Many polymers used to thicken compositions are ineffective in high ionic strength compositions, thus are not suitable for use with bleach. Other hypochlorite compositions of the prior art are thickened with surfactants and may exhibit hypochlorite stability problems. Surfactant thickening systems also are not cost effective when used at the levels necessary to obtain desired product viscosity values.
Polymer-thickened hypochlorites are disclosed or described in several references. U.S. Pat. No. 4,011,172 issued to Marsan et al discloses clay thickened hypochlorite and suggests that polyacrylamides may also be suitable. Briggs, U.S. Pat. No. 3,663,442 discloses bleach including a styrene/acrylic acid polymer. The polymer is formulated as an insoluble particulate for opacification rather than thickening. Rupe et al, U.S. Pat. No. 4,116,851 shows a clay thickened hypochlorite bleach which could include polymeric thickening agents such as polystyrene, polypropylene, polyethylene or copolymers of styrene with e.g., acrylate, maleate or vinyl acetate. Such polymers are disclosed in particulate form, however, and apparently thicken only in conjunction with the inorganic clays. U.S. Pat. No. 4,438,016 issued to Kiewert et al discloses a hypochlorite cleanser containing amine oxides and paraffin sulfonates, and thickened by calcium aluminum silicates and optionally by acrylate or methacrylate copolymers. Zimmerer et al, U.S. Pat. No. 3,393,153 shows non-thickened hypochlorite bleach compositions which stably suspend optical brighteners aided by various insoluble polymers. Sabatelli, U.S. Pat. No. 4,147,650 shows a hypochlorite solution thickened with a combination of metasilicates and polyacrylate or polymethacrylate having a high average molecular weight, as typical of the prior art. Hynam et al, U.S. Pat. No. 3,684,722 discloses a thickened bleaching composition of amine oxides or betaines, an alkali-metal soap, an alkali metal hypochlorite and, optionally, caustic. Hynam et al mentions that polymers such as polyacrylates were tested for their ability to thicken the hypochlorite but no lasting thickening was achieved. French Pat. No. 78 23943 describes a non-surfactant, polymeric thickened hypochlorite composition. This patent illustrates the ineffectiveness of polymer thickeners of the art, as high levels of polymers such as polyacrylate (25% or more) are required to attain a moderate, one hundred centipoise (cP) thickening. Polyacrylates are generally shown in the art cited above to be unstable in hypochlorite solutions. Other references, such as Joy, U.S. Pat. No. 4,229,313 disclose surfactant thickened bleach compositions.
None of the prior art has successfully addressed the problem of developing a pourable, highly thickened, bleaching cleanser. The prior art is further deficient in teaching a bleach-stable cleanser capable of relatively high viscosity values, on the order of 300 cP and higher, and achieving such values with low levels of a polymeric/surfactant thickening system utilizing a relatively low molecular weight polymer.